Conventionally, high-frequency filters and other high-frequency circuit devices including a resonant body as a basic element are essential for communication systems. With a resonant body, among resonator bodies, using a dielectric material such as a high dielectric constant, low-loss ceramic material, a high-frequency circuit device functioning as a small and low-loss (high-Q) resonator can be achieved.
Such a resonator can be disposed with other circuit elements such as an amplifier, an oscillator, and a mixer circuit on a substrate to make a high-frequency circuit have a module configuration. In this case, a high-frequency signal needs to be input/output to/from the resonator via a transmission line such as a stripline on the substrate. As an example of such high-frequency circuits using a dielectric material, a circuit in which a dielectric member is disposed on a circuit board and then a stripline around the member and thereby a high-frequency signal is input/output from/to a resonator is known, as disclosed, e.g., in Japanese Unexamined Patent Publication 10-284946.
In this case, the dielectric member has a circular cross section and resonates in the TE01δ mode. The dielectric member is used for the purpose of transmitting only a desired frequency element of a high-frequency signal from the stripline, or removing unnecessary frequency elements.
Problems to be Solved
However, the above-described known high-frequency circuit in which a dielectric member is disposed on a substrate has the following problems.
First, since the dielectric member is used without being shielded, high-frequency signals (electromagnetic waves) from the dielectric member are emitted. The signal emission may cause an increase in the loss of a resonator, i.e., a reduction in the Q value of the resonator. Moreover, by the emitted electromagnetic waves, the dielectric member may be coupled with other circuits disposed on a substrate to make circuit operation unstable. Furthermore, in order to suppress the coupling between the dielectric member and other circuits by the emitted electromagnetic waves, it is necessary to dispose the dielectric member so as to be spaced apart from the other circuits by a certain distance. This is an obstacle to reduce the size of an entire module.
The above-described problems are more clearly noticed, as the frequency of high-frequency signals dealt with in a high-frequency circuit device is increased. Therefore, they may be fatal problems in a millimeter wave band or the like.
Moreover, in a TE01δ mode resonator, the distribution of the resonant electric field may show a concentric configuration in a cylindrical dielectric member. Therefore, it may be difficult to obtain a desired coupling of the dielectric member with a stripline or the like disposed on the substrate.